Understanding Shutter Speed

Shutter Speed

Shutter speed is a measurement of time that a camera's shutter is open—allowing light, usually after it has passed through a lens and through the aperture diaphragm, to strike a photosensitive surface, like film or a digital sensor.

Unlike the nuances of aperture and its relation to light and optics, shutter speed is much more of a straightforward affair. Because of this, permit me to take you off on a bit of a tangent so that we can talk about how camera shutters work.

The challenge of the mechanics of the shutter is in designing a device that exposes the entire sensor or film plane to an equal number of photons so that exposure is consistent through the image. Many people think that the shutter works like a miniature garage door. If you can visualize a garage door opening and then closing in front of a photosensitive surface, you can see that the problem with that design is that the bottom of the image will be exposed to more photons of light as it is the first portion of the image to see light as the door begins to open and it is also the last part to be blocked by the door as the door closes. Therefore, a photo taken with a shutter that functions like a door will have an unbalanced exposure.

There have been several different designs of camera shutters over the years. The very first cameras had lens-cap-type shutters where the lens was exposed to light by removing the cap and then, after a calculated amount of time, the cover was placed back over the lens. Exposures back then took several minutes, and even hours, so the relatively slow opening and closing of the "shutter" was not problematic.

At the inexpensive end of the spectrum, the simple leaf shutter appears on many disposable and point-and-shoot cameras of yesterday. This is a mechanized version of the old lens cap "shutter" where a leaf, or two leaves, are mechanically pulled aside to let light through an opening. They generally only operate at one speed.

The leaf shutter, also known as a diaphragm shutter, functions very much like the aperture diaphragm of the lens in that a group of metal blades is mechanically opened and closed in rapid fashion. Unlike the blades of the aperture diaphragm that just constrict to a small opening, these blades close all the way until there is no light coming through the shutter. The shutters are designed to open and close extremely fast so that the center of the image does not see an appreciably greater amount of light than the edges. Because of their design, leaf shutters work very well when synchronized with flash strobes, but cannot operate at speeds as fast as the shutter type that we will discuss next.

Almost all modern SLR and DSLR cameras employ the focal-plane shutter. The focal-plane shutter works more like a garage door, but with a second door, called acurtain, that follows behind the first curtain to close the image sensor or film off from light after the first curtain opens. This two-curtain design allows a balance of light across the sensor or film so that exposure is even. This design allows for extremely fast operation, up to 1/8000 of a second, on today's SLR and DSLR cameras. However, focal-plane shutters, due to their complexity and exotic construction, are relatively expensive.

Like most things, the shutter has gone digital. Many modern digital cameras operate an electronic shutter that simply powers the digital sensor on for a selected amount of time. Because there is no mechanical function, electronic shutter speeds can be extremely fast. A global shutter turns the entire sensor on and off at once, while a rolling shutter activates one row of pixels at a time across its width.

Both the focal-plane shutter and rolling electronic shutter, because of their design and function, can cause interesting distortion through an image when there is fast motion across the picture plane.

OK, back to shutter speeds. As I wrote earlier, shutter speed is simply a measure of time that the shutter is open, or, in the case of the electronic shutter, the sensor is powered. The longer the shutter is open, the more light comes through. No inverse square law here (thank goodness!); if you double the amount of time that the shutter is open, you will double the amount of light coming in. Shutter speed is simple, right?

How does this relate to exposure and the exposure values (EVs) that we discussed in the first lesson? Because of the linear nature of the relationship of photons entering the camera to shutter speed, we can use shutter speed to easily and precisely change the amount of light hitting our photosensitive surface. By slowing the shutter speed, from 1/30th of a second to 1/15th of a second, for instance, we will double the amount of light passing through the shutter. This doubling of light is identical to the doubling of light accomplished by opening aperture, albeit by a different mechanical function, and represents a +1 EV shift. Changing the shutter speed from 1/2000th of a second to 1/4000th of a second then halves the amount of light coming through the shutter and represents a -1 EV shift.

digital photography- Shutter speed..

What is shutter speed...?????

The camera's shutter speed, the lens's brightness (f-number), and the scene's luminance together determine the amount of light that reaches the film or sensor (the exposure). Exposure value (EV) is a single quantity that accounts for the shutter speed and the f-number.

Multiple combinations of shutter speed and f-number can give the same exposure value. Doubling the exposure time doubles the amount of light (subtracts 1 EV). Making the f-number one stop brighter (reducing the f-number by a factor of ) also doubles the amount of light. A shutter speed of 1/50 s with an f/4.0 lens gives the same exposure value as a 1/100 s shutter with an f/2.8 lens, and also the same exposure value as a 1/200 s shutter with an f/2.0 lens.

In addition to its effect on exposure, the shutter speed changes the way movement appears in photographs. Very short shutter speeds can be used to freeze fast-moving subjects, for example at sporting events. Very long shutter speeds are used to intentionally blur a moving subject for artistic effect.^[2] Short exposure times are sometimes called "fast", and long exposure times "slow".

Adjustment to the aperture controls the depth of field, the distance range over which objects are acceptably sharp; such adjustments need to be compensated by changes in the shutter speed.

In early days of photography, available shutter speeds were not standardized, though a typical sequence might have been 1/10 s, 1/25 s, 1/50 s, 1/100 s, 1/200 s and 1/500 s. Following the adoption of a standardized way of representing aperture so that each major step exactly doubled or halved the amount of light entering the camera (f/2.8, f/4,f/5.6, f/8, f/11, f/16, etc.), a standardized 2:1 scale was adopted for shutter speed so that opening one aperture stop and reducing the shutter speed by one step resulted in the identical exposure. The agreed standards for shutter speeds are:^[3]

• 1/1000 s
• 1/500 s
• 1/250 s
• 1/125 s
• 1/60 s
• 1/30 s
• 1/15 s
• 1/8 s
• 1/4 s
• 1/2 s
• 1 s

An extended exposure can also allow photographers to catch brief flashes of light, as seen here. Exposure time 15 seconds.

With this scale, each increment roughly doubles the amount of light (longer time) or halves it (shorter time).

Camera shutters often include one or two other settings for making very long exposures:

• B (for bulb) keeps the shutter open as long as the shutter release is held.
• T (for time) keeps the shutter open until the shutter release is pressed again.

The ability of the photographer to take images without noticeable blurring by camera movement is an important parameter in the choice of slowest possible shutter speed for a handheld camera. The rough guide used by most 35 mm photographers is that the slowest shutter speed that can be used easily without much blur due to camera shake is the shutter speed numerically closest to the lens focal length. For example, for handheld use of a 35 mm camera with a 50 mm normal lens, the closest shutter speed is 1/60 s. This rule can be augmented with knowledge of the intended application for the photograph, an image intended for significant enlargement and closeup viewing would require faster shutter speeds to avoid obvious blur. Through practice and special techniques such as bracing the camera, arms, or body to minimize camera movement longer shutter speeds can be used without blur. If a shutter speed is too slow for hand holding, a camera support, usually a tripod, must be used. Image stabilization can often permit the use of shutter speeds 3–4 stops slower (exposures 8–16 times longer).

Shutter priority refers to a shooting mode used in semi-automatic cameras. It allows the photographer to choose a shutter speed setting and allow the camera to decide the correct aperture. This is sometimes referred to as Shutter Speed Priority Auto Exposure, or TV (time value) mode.

What is shutter speed...?????

The camera's shutter speed, the lens's brightness (f-number), and the scene's luminance together determine the amount of light that reaches the film or sensor (the exposure). Exposure value (EV) is a single quantity that accounts for the shutter speed and the f-number.

Multiple combinations of shutter speed and f-number can give the same exposure value. Doubling the exposure time doubles the amount of light (subtracts 1 EV). Making the f-number one stop brighter (reducing the f-number by a factor of ) also doubles the amount of light. A shutter speed of 1/50 s with an f/4.0 lens gives the same exposure value as a 1/100 s shutter with an f/2.8 lens, and also the same exposure value as a 1/200 s shutter with an f/2.0 lens.

In addition to its effect on exposure, the shutter speed changes the way movement appears in photographs. Very short shutter speeds can be used to freeze fast-moving subjects, for example at sporting events. Very long shutter speeds are used to intentionally blur a moving subject for artistic effect.^[2] Short exposure times are sometimes called "fast", and long exposure times "slow".

Adjustment to the aperture controls the depth of field, the distance range over which objects are acceptably sharp; such adjustments need to be compensated by changes in the shutter speed.

In early days of photography, available shutter speeds were not standardized, though a typical sequence might have been 1/10 s, 1/25 s, 1/50 s, 1/100 s, 1/200 s and 1/500 s. Following the adoption of a standardized way of representing aperture so that each major step exactly doubled or halved the amount of light entering the camera (f/2.8, f/4,f/5.6, f/8, f/11, f/16, etc.), a standardized 2:1 scale was adopted for shutter speed so that opening one aperture stop and reducing the shutter speed by one step resulted in the identical exposure. The agreed standards for shutter speeds are:^[3]

• 1/1000 s
• 1/500 s
• 1/250 s
• 1/125 s
• 1/60 s
• 1/30 s
• 1/15 s
• 1/8 s
• 1/4 s
• 1/2 s
• 1 s

An extended exposure can also allow photographers to catch brief flashes of light, as seen here. Exposure time 15 seconds.

With this scale, each increment roughly doubles the amount of light (longer time) or halves it (shorter time).

Camera shutters often include one or two other settings for making very long exposures:

• B (for bulb) keeps the shutter open as long as the shutter release is held.
• T (for time) keeps the shutter open until the shutter release is pressed again.

The ability of the photographer to take images without noticeable blurring by camera movement is an important parameter in the choice of slowest possible shutter speed for a handheld camera. The rough guide used by most 35 mm photographers is that the slowest shutter speed that can be used easily without much blur due to camera shake is the shutter speed numerically closest to the lens focal length. For example, for handheld use of a 35 mm camera with a 50 mm normal lens, the closest shutter speed is 1/60 s. This rule can be augmented with knowledge of the intended application for the photograph, an image intended for significant enlargement and closeup viewing would require faster shutter speeds to avoid obvious blur. Through practice and special techniques such as bracing the camera, arms, or body to minimize camera movement longer shutter speeds can be used without blur. If a shutter speed is too slow for hand holding, a camera support, usually a tripod, must be used. Image stabilization can often permit the use of shutter speeds 3–4 stops slower (exposures 8–16 times longer).

Shutter priority refers to a shooting mode used in semi-automatic cameras. It allows the photographer to choose a shutter speed setting and allow the camera to decide the correct aperture. This is sometimes referred to as Shutter Speed Priority Auto Exposure, or TV (time value) mode.